Fluid filter elements, including filters for liquids and gases, are in widespread use. One particular class of fluid filter element is the axial flow filter. The axial flow filter element is typically formed by wrapping or coiling a pleated sheet of filter media to form a multilayer filter body. In axial flow filters the fluid stream enters the filter element at one end face of the filter, is processed through the filter media and then exits the filter element at an axially opposing end face of the filter.
As an example of an axial flow filter, U.S. Published Patent application 2007/0271886 (Rieger et. al) discloses an axial flow filter element having at least one flat filtering element wrapped or coiled into a compact body configured to filter fluid media flowing generally axially between two end faces of the filter element. The filter element is formed of at least one layer of corrugated or pleated filter paper and a layer of smooth un-corrugated filter paper. The layers are bonded together and then tightly wrapped together to form an axial flow filter element of the desired shape and size.
Filters experience fluid flow induced stress on the filter media layers during operation. The flow induced stress may be severe in certain cases, for example, when the flow rate is very high, when the filter is perhaps substantially fouled with debris. In the case of an axial flow air filter in service during abnormal operating conditions in which the filter element becomes wetted with water, the flow induced stress may become severe. The formation of elevated axial stresses in filter elements due to abnormal operating conditions may result in the potentially compromise the structural or adhesive bonds between the wrapped layers of the filter element. In rare cases where the bonds are severely compromised this may lead to telescopic deformation of the filter medium or other deformations of the filer element.
Time-consuming and expensive manufacturing and engineering solutions have been employed to resolve this problem, including the addition of a plastic grid support structure on the clean side of the filter element, as well as various formulations of adhesives between filter element layers, filter housings incorporating filter element support structures and the like. While such techniques are useful in overcoming the problem, they are less than optimal from a filter cost and filter component complexity standpoint and therefore the need exists for a cost effective solution.